Using a liquid smoke composition as a replacement for smoking food by direct contact with wood smoke has become a standard industry practice. When applied to the surface of meats and other proteinaceous foodstuffs, a liquid smoke composition imparts a characteristic smoke flavor and a dark smoked color to a foodstuff. The preparation of a smokehouse-like foodstuff by applying an aqueous liquid smoke composition to a foodstuff requires controlling and balancing many related variables, such as the foodstuff composition, temperature, humidity, process and contact time, and amount and concentration of applied liquid smoke composition.
Wood smoke itself is a complex and variable mixture of compounds produced during wood pyrolysis, and includes numerous vaporous compounds which are liquids at room temperature. Pyrolysis is a general term for the thermal decomposition of an organic material, such as wood, plants, and fossil fuels, either during combustion or by rapid heating in an oxygen-deleted atmosphere. Pyrolysis with combustion uses the oxidation or burning of a portion of the organic material to provide the thermal energy required to vaporize and decompose the remainder of the organic material. For pyrolysis without combustion, thermal energy is supplied indirectly from an external source, such as radiation, solid or gaseous heat carriers, or thermal conduction through reactor walls. The energy supplied by an external source vaporizes and decomposes the organic material without directly burning the organic material.
One commercial liquid smoke preparation is the aqueous liquid smoke composition described in Hollenbeck U.S. Pat. No. 3,106,473. This composition is produced by partial combustion of hardwood sawdust with limited access to air, followed by collecting the desirable smoke constituents in water. A heavy, water-insoluble phase, which contains tar, polymers, polycyclic aromatic hydrocarbons, waxes, and other undesirable products unsuitable for use in food applications is discarded. This type of composition is termed a "slow pyrolysis" liquid smoke composition.
Another commercial liquid smoke preparation is disclosed in Underwood et al. U.S. Pat. No. 4,876,108. This composition is produced by rapidly heating ground wood or cellulose in an oxygen-starved atmosphere, and collecting the water-soluble pyrolysis products. This type of composition is termed a "fast pyrolysis" liquid smoke composition. Like a slow pyrolysis composition, a fast pyrolysis composition contains tar, polymers, and hydrocarbons that must be separated and discarded.
Both methods of pyrolysis produce liquids (i.e., condensable vapors), gases (i.e., noncondensable vapors), and solids (i.e., char and ash) in varying proportions depending upon feed material and pyrolysis conditions. The condensed liquids are further subdivided into water-soluble organic compounds and water-insoluble tars. It is known that the desirable active ingredients for flavoring and coloring foodstuffs are present in the water-soluble condensed liquids. The water-insoluble tars have been considered a by-product of wood pyrolysis that are of little to no value, and typically are discarded.
While there are hundreds of different chemical species present in liquid smoke compositions, the useful water-soluble components of a liquid smoke composition generally are divided into classes based on compounds having distinct functional groups. These classes are acids, carbonyls, phenolics, and basic and neutral constituents. In general, phenolics are the primary flavoring compounds, carbonyls are the primary coloring compounds, and acids are primarily preservatives and pH controlling agents. The acids and carbonyls also make a secondary contribution to flavor and enhance the surface characteristics of smoked foodstuffs. The acids are predominantly C.sub.1 -C.sub.4 carboxylic acids, and mainly acetic acid. Acids are measured as titratable acidity calculated as percent acetic acid, by weight.
For commercial aqueous liquid smoke compositions, production begins with smoke generated by the combustion and/or pyrolysis of wood as discussed above. After pyrolysis, the smoke is collected, and, can be fed through a column countercurrent to a flow of recirculating water. Alternatively, smoke components can be condensed directly to form a liquid, then water is added to the condensed smoke components. Dilution of condensable smoke components with water by either method results in the separation of undesirable tars, polymers, and other water-insoluble components from the desirable liquid smoke components.
In the preparation of a commercial liquid smoke composition, additional water-insoluble tars separate from the liquid smoke composition while the liquid smoke composition is held in storage. Water-insoluble hydrocarbons, like polynuclear aromatic compounds, are unavoidable contaminants associated with the pyrolysis of wood, and settle out of the liquid smoke composition with the tar. The hydrocarbons, like the tar, are physically separated from the liquid smoke composition. The water-insoluble tar then is discarded.
However, due to the presence of organic compounds in the liquid smoke composition, the tars and hydrocarbons do not completely settle out of the composition. If the organic compound content of the liquid smoke solution is low, some tar is dispersed, or suspended, in the liquid smoke composition. As the organic compound concentration of the liquid smoke composition increases, a portion of the tar actually can be dissolved in the liquid smoke composition. Removing the dissolved tar and hydrocarbons has been difficult to impossible to achieve, especially because tar is continually formed from monomeric tar precursors during storage of the liquid smoke composition.
Attempts have been made to remove dissolved tar from a liquid smoke composition by preparing a tar-depleted liquid smoke composition. It should be understood that a tar-depleted liquid smoke composition is not essentially free of dissolved tars. Dissolved tar is present in a tar-depleted liquid smoke composition because a portion is solubilized in, or dispersed by, the organic components of the liquid smoke composition, and because a portion of new tar, which is formed over time, is dissolved in the composition.
One type of tar-depleted liquid smoke composition is disclosed in Nicholson U.S. Pat. No. 4,431,033. These tar-depleted liquid smoke compositions are prepared by contacting a liquid smoke composition with a water-insoluble organic solvent, like methylene chloride, to extract dissolved tar from the aqueous composition. The resulting tar-depleted liquid smoke composition has an absorptive power of at least 0.25 at 340 nm (nanometers).
Another type of tar-depleted liquid smoke composition is disclosed in Chiu U.S. Pat. No. 4,592,918. These liquid smoke compositions have an absorptive power of at least about 0.25 at 340 nm, and a percent light transmittance (% T) at 590 nm of at least about 50%. The tar-depleted liquid smoke is prepared by partially neutralizing a liquid smoke composition to a pH above 4 to precipitate dissolved tars, or by extracting dissolved tar from the liquid smoke composition with a nonpolar solvent.
Moeller U.S. Pat. No. 5,637,339 also discloses a tar-depleted liquid smoke prepared by contacting the liquid smoke with activated charcoal.
Although the above-described disclosures teach how to reduce dissolved tar content, the goal of a liquid smoke composition that is essentially free of dissolved tar has not been achieved. The tar-depleted liquid smoke compositions prepared by the above-discussed methods typically are stored under refrigeration to retard formation of dissolved tar which darkens the composition and yields a water-insoluble tar precipitate after dilution with water. The water-insoluble tar precipitate is often observed as turbidity when the liquid smoke composition is diluted with water. Therefore, the tar and tar precursors remaining in the above-described tar-depleted liquid smoke compositions pose continued problems to users of liquid smoke compositions.
In particular, the water-insoluble tars that form during storage of a liquid smoke composition or a tar-depleted liquid smoke compositions are intractable, high viscosity liquids or semisolids. Such tars precipitate to the bottom of storage containers, or cling to the sides of the container, and therefore, pose no problem when the liquid smoke composition is removed from the container for use.
However, dissolved tars do pose a problem. In many applications, the liquid smoke composition is diluted with water before application to a foodstuff, like a meat or a casing. Water dilution reduces the concentration of organic compounds, and the diluted liquid smoke composition no longer has sufficient dispersing or solvating properties to maintain the dissolved tars in suspension or solution. Accordingly, a fine tar precipitate forms in the diluted liquid smoke composition and the diluted liquid smoke composition has a turbid appearance.
The fine tar precipitate may or may not adversely affect the foodstuff being treated with the diluted liquid smoke. However, the fine tar precipitate does adversely affect application equipment, like clogging spray nozzles and filters, and building up on casing peelers to reduce productivity.
The present invention is directed to stabilized liquid smoke compositions that overcome the problems associated with prior liquid smoke compositions, and with prior tar-depleted liquid smoke compositions, by eliminating the formation of dissolved tars during storage.